The present invention relates to gas turbine engines having convergent/divergent nozzles, and more particularly to a cooled divergent seal arrangement.
An exhaust nozzle optimizes the thrust produced within a gas turbine engine. In augmented gas turbine engines, convergent/divergent (C/D) nozzles provide a multitude of nozzle positions. Flaps circumferentially distributed aft of the augmentor or exhaust duct form the convergent and divergent sections for which the nozzle is named. Flap seals disposed between adjacent flaps minimize gas leakage between flaps in both sections. The convergent section is pivotally connected to the augmentor or exhaust duct and to the divergent section. The divergent section is pivotally connected to the convergent section and to an external fairing positioned radially outboard of the divergent section. The opposite end of the external fairing is pivotally attached to a static outer casing which surrounds a portion of the nozzle. Together, the outer casing, the convergent and divergent sections, and the external fairing form a nozzle plenum.
Because of the high temperature of the core gas exiting the turbine and augmentor, exhaust nozzles are cooled with air bled at a lower temperature and a higher pressure than that of the exhaust gas flow passing through the nozzle system. Cooling air enters the exhaust gas path within the augmentor or exhaust duct via cooling holes in the augmentor or exhaust duct liner and subsequently passes into the nozzle system as a layer of cooling airflow along the inner surface or “hot side” of the nozzle flaps and seals. Cooling airflow within the nozzle plenum also cools the “cold side” side of the flaps and flap seals.
Conventional nozzle systems employ geometry to seal between a cooling liner body and the nozzle system convergent section flaps and flap seals. Traditionally, a columbium alloy (Nb) is utilized as the material of choice for its inherit low Coefficient or Thermal Expansion (CTE). However, Nb may have limited strength and may require difficult to process and maintain coatings. Raw material costs and current lead-time for procurement of Nb is also relatively significant.
Accordingly, it is desirable to provide effective cooling of a cooling liner main body convergent section interface with materials which are less expansive to manufacture yet provide increased durability.